1. Field of the Invention
The present invention relates to a position sensible liquid crystal display device, and more particularly, to a position sensible liquid crystal display (PSLCD) device suitable for automatic compensation of potential distribution distortions of a driving signal.
2. Discussion of the Related Art
In general, as shown in FIG. 1, a liquid crystal display (LCD) device includes an upper plate 3, a lower plate 1, and a liquid crystal sealed between the upper and lower plates. The upper plate 3 has a common electrode 6, a layer of black matrix 4, and a layer of R (red), G (green), and B (blue) color filters 5 that filter light to generate colors. The lower plate has a plurality of data lines and scanning lines arranged at right angles to each other and spaced at fixed intervals to form a matrix of pixel regions. Each of the pixel regions has a thin film transistor and a pixel electrode. More particularly, lower plate 1 has thin film transistors 2 disposed thereon at fixed intervals, each with a gate electrode G corresponding to a scanning line, a source electrode S, and a drain electrode D (corresponding to a data line). Each of the pixel regions has a pixel electrode 2a connected to the drain electrode D of the thin film transistor 2. Black matrix 4 on the upper plate 3 blocks light in sections other than pixel electrodes 2a, which corresponds to the R, G, and B color filters 5. Upon selective application of driving signals from external driving circuits to the scanning lines and the data lines, the LCD device displays an image.
A conventional PSLCD device will be explained with reference to the attached drawings. FIG. 2 is a plan view of an upper plate of the conventional PSLCD. A conventional PSLCD device includes color filters, a common electrode of an ITO layer, and, as explained below, the black matrix. As shown in FIG. 2, the black matrix in the conventional PSLCD includes first black matrix elements 21 connected in vertical and horizontal directions in a grid arrangement. Second black matrix elements (not shown in FIG. 2) are used to block light to portions other than the pixel regions between black matrix elements 21. Black matrix 21 has a plurality of equipotential compensating resistors 22 connected and extending in each direction (directions of the data lines and the scanning lines), and the equipotential compensating resistors 22 of the same direction are connected to an equipotential maintaining resistor 23. Typically, not every pixel has matrix element 21 opposite to it, but instead, multiple pixels may be between a single line of black matrix grid 21. Lines of the first black matrix element 21, connected in series in X-axis direction, are called the X-axis grid and lines of the first black matrix element 21, connected in series in the Y-axis direction, are called a Y-axis grid. A driving signal for detecting X- and Y-axis coordinates of a stylus are applied through the first black matrix elements 21 connected in series, i.e., through the X- and Y-axes grids. The equipotential maintaining resistors 23 are provided at four sides of the PSLCD device, and a driving AC signal applying part 24 is provided at each of four corners of the PSLCD where the equipotential maintaining resistors 23 at the four sides are met for applying the driving AC signal.
FIG. 3 is a circuit diagram illustrating a driving signal applying device for applying a driving signal for detecting position in the conventional PSLCD device. As shown, the driving signal applying device includes an analog switching part 31 and buffer sections 32 that apply either a driving AC signal or a grounding signal to the corner applying areas.
The operation of the aforementioned conventional PSLCD device will now be explained.
Referring to FIGS. 2 and 3, in order to apply a driving AC signal to the X- and Y-axis grids of black matrix elements for position detection, a microcontroller selects appropriate driving signal applying areas 24 to apply the driving AC signal and a grounding signal, and operates analog switch 31 accordingly. The analog switch has a driving AC signal terminal and a ground terminal, either of which may be selected in response to selecting signals from the microcontroller. The selected driving AC signal or the grounding signal is provided to the driving signal applying area 24 through buffer amplifying parts 32.
Deviations in the signal line resistances, through which the AC signal is applied, results in unequal voltage drops in the X and Y axis directions, and thus causes a deterioration in performance.
In particular, the equipotential compensating resistors 22, equipotential maintaining resistors 23, and supplementary resistors have deviations in their performances from intended performances due to process errors; and the instances of contact elements between the lower plate through the upper plate are not identical due to irregularities in bonding.
Thus, the application of the driving signal and the grounding signal to the driving signal applying area, without any adjustment in the applied signals, results in signal distortion and corresponding degradation in position detection.